全文获取类型
收费全文 | 3822篇 |
免费 | 67篇 |
国内免费 | 25篇 |
专业分类
化学 | 2141篇 |
晶体学 | 36篇 |
力学 | 77篇 |
数学 | 588篇 |
物理学 | 1072篇 |
出版年
2020年 | 23篇 |
2019年 | 25篇 |
2018年 | 26篇 |
2017年 | 25篇 |
2016年 | 48篇 |
2015年 | 47篇 |
2014年 | 56篇 |
2013年 | 171篇 |
2012年 | 166篇 |
2011年 | 204篇 |
2010年 | 88篇 |
2009年 | 76篇 |
2008年 | 177篇 |
2007年 | 175篇 |
2006年 | 148篇 |
2005年 | 180篇 |
2004年 | 135篇 |
2003年 | 129篇 |
2002年 | 107篇 |
2001年 | 72篇 |
2000年 | 71篇 |
1999年 | 51篇 |
1998年 | 38篇 |
1997年 | 45篇 |
1996年 | 61篇 |
1995年 | 57篇 |
1994年 | 59篇 |
1993年 | 62篇 |
1992年 | 60篇 |
1991年 | 34篇 |
1990年 | 40篇 |
1989年 | 57篇 |
1988年 | 57篇 |
1987年 | 48篇 |
1986年 | 41篇 |
1985年 | 80篇 |
1984年 | 66篇 |
1983年 | 49篇 |
1982年 | 68篇 |
1981年 | 50篇 |
1980年 | 58篇 |
1979年 | 53篇 |
1978年 | 64篇 |
1977年 | 55篇 |
1976年 | 68篇 |
1975年 | 39篇 |
1974年 | 49篇 |
1973年 | 49篇 |
1972年 | 28篇 |
1968年 | 22篇 |
排序方式: 共有3914条查询结果,搜索用时 31 毫秒
81.
Abstract— C18 formate ester (5) [2-(6-methyl-8-(2,6,6-trimethyl-1-cyclohexen-1-yl)-3E,5E,7E-octatrienyl formate], a highly reactive analog of retinal, was synthesized and its interaction with bacterioopsin studied. The formate ester, in the absence of purple or bleached membrane, undergoes very rapid reaction (tl/2 = 0.9 min) in neutral buffer but with membrane present it diffuses more rapidly into the membrane where it reacts slowly. Incorporation of 5 in the membrane results in a 38 nm (3900 cm-1 ) red shift which remains after reconstitution with retinal. Similar experiments with the corresponding C18 alcohol (4) results in a red shift, but this absorption blue shifts upon reconstitution with retinal. Washing the formate ester-treated membrane with bovine serum albumin or the corresponding lyophilized preparation with hexane, treatments that remove retinal oxime, fails to remove the UV-visible absorption, suggesting that a covalent bond between the C18 moiety and a nucleophilic group of the protein has probably formed. 相似文献
82.
D. Fennell Evans Martin Allen B. W. Ninham Abdel Fouda 《Journal of solution chemistry》1984,13(2):87-101
Critical micelle concentrations were determined by conductance measurements for decyl-, dodecyl-, tetradecyl- and hexadecyltrimethylammonium bromide in water at 25, 60, 95, 130, and 160°C. The results are discussed in terms of the equilibrium model and the nonlinear Poisson-Boltzmann model for micelle formation. The free energies of transferring a methylene group from water to the oil-like interior of the micelle are found to be –781 at 25°C, –796 at 60°C, –819 at 95°C, –815 at 130°C, and –787 at 160°C cal-mol–1. 相似文献
83.
A method for determining the oxygen content of the high-temperature superconductor YBa2Cu3O6.5+x is described. The superconductor is dissolved in 4.4 M hydrobromic acid, forming bromine. The mixture is then diluted with hydrochloric acid to obtain a solution of bromine and Cu(II) in 0.44 M hydrobromic acid and 1.1 M hydrochloric acid. As(III) is added in slight excess of that required to react with the bromine and the unreacted As(III) is determined by titration with potassium bromate. Oxygen does not interfere. The results of this method are in agreement with those of other iodimetric procedures. The dissolution of the superconductor in 4.4 M hydrobromic acid is much faster than in hydrochloric acid, the medium used in one iodimetric technique. YBa2Cu3O6.5+x sintered fibers and powder samples weighing from ca. 0.5 to 200 mg were analyzed for oxygen content. 相似文献
84.
85.
86.
87.
Abe K Abt I Ahn CJ Akagi T Allen NJ Ash WW Aston D Baird KG Baltay C Band HR Barakat MB Baranko G Bardon O Barklow T Bazarko AO Ben-David R Benvenuti AC Bienz T Bilei GM Bisello D Blaylock G Bogart JR Bolton T Bower GR Brau JE Breidenbach M Bugg WM Burke D Burnett TH Burrows PN Busza W Calcaterra A Caldwell DO Calloway D Camanzi B Carpinelli M Cassell R Castaldi R Castro A Cavalli-Sforza M Church E Cohn HO Coller JA Cook V Cotton R Cowan RF Coyne DG D'Oliveira A Damerell CJ Daoudi M 《Physical review D: Particles and fields》1995,52(7):4240-4244
88.
Ann M. Schmiedekamp Igor A. Topol Stanley K. Burt Holy Razafinjanahary Henry Chermette Timothy Pfaltzgraff Christopher J. Michejda 《Journal of computational chemistry》1994,15(8):875-892
The consistency of three density functional computational implementations (DMol, DGauss, and deMon) are compared with high-level Hartree–Fock and Møller–Plesset (MP) calculations for triazene (HN?NNH2) and formyl triazene (HN?NNHCOH). Proton affinities on all electronegative sites are investigated as well as the geometries of the neutral and protonated species. Density functional calculations employing the nonlocal gradient corrections show agreement with MP calculations for both proton affinities and geometries of neutral and protonated triazenes. Local spin density approximation DMol calculations using numerical basis sets must employ an extended basis to agree with other density functional codes using analytic Gaussian basis sets. The lowest energy conformation of triazene was found to be nonplanar; however, the degree of nonplanarity, as well as some bond lengths, is dependent on the basis set, electron correlation treatment, and methods used for the calculation. © 1994 by John Wiley & Sons, Inc. 1 This article is a U.S. Government work and, as such, is in the public domain in the United States of America. 相似文献
89.
90.